Treatment of ammonium nitrate explosives



Patented Jan; 31,1939

TREATMENT OF AMIVIONIUM NI'I'BATE EXPLOSIVES William E. Kirst,.Woodbury, N. J., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 30, 1937, Serial No. 156,495

, 4' Claims.

This invention relates to a method of treating explosive compositions comprised largely of ammonium nitrate, and particularly to a method of heat treating compositions containing ammonium nitrate as the principal ingredient, together with sensitizing agents, whereby an improvement in the explosive properties of the composition is obtained.

There are two important types of explosives in which ammonium nitrate has been employed, one of which is that of the common ammonia dynamites containing nitroglycerin, in which this latter compound serves as the principal explosive ingredient or as the sensitizer, while ammonium nitrate is used to replace or supplement nitroglycerin. In a. second type, ammonium nitrate is mites of the ammonia permissible and similar types are readily detonated by means of a commercial blasting cap, even when containing as high as 80% ammonium nitrate, there are ammonium' nitrate high explosives in widespread use that are so insensitive that they can not be initiated by the action of a blasting cap or a line of Cordeau. These explosives are capable, however, of propagating the explosion with undiminished velocity throughout their column after detonation has once been initiated, provided a sufliciently large diameter column of explosive is used.

In all its compositionaammonium nitrate has the property of being readily afiected by water, in liquid or vaporous form, because of the hygroscopic nature of the material. of even a small friction of a percent ofwater, ammonium nitrate after continued storage tends to become hard or set, due to the solution and recrystallizing processes that take place between the crystals. When set in a hard mass, compositions normally sensitive .to the action of a cap or to propagation of the explosion wave throughout-the column become insensitive and incapable of functioning satisfactorily. For this reason, ammonium nitrate explosives must .be effectively protected against water and, 'moisture. In the case of some compositions high in ammonium nitrate; where the maintenance of a well-defined sensitiveness range is desired,- the explosive has been enclosed in waterproof metal ample 0;90.

In the presence containers; Loss of sensitiveness results also when the density of the ammonium nitrate material exceeds a certain maximum limit.

The object of this invention is a method for physically treating ammonium nitrate explosive compositions, whereby the properties'of the finished explosive are favorably affected. A further object is a heating treatment for. such compositions, whereby improvement in sensitivenessand velocity results. A still further object is such a method whereby an equalization of density of ammonium nitrate compositions results. Additional objects will be disclosed as the invention is described at length hereinafter.

I have found that the foregoing objects are accomplished in the case of explosive compositions of relatively-high density including ammonium nitrate as the principal ingredient and at least one normally solid fusible organic sensitizer by treating said explosive compositions according to the process of our invention, which comprises heating saidcomposition under conditions of confinement to a temperature at which said sensitizing agent is in the liquid state, and subsequently cooling said composition. The process is most efiective with ammonium nitrate compositions having a relatively high density, for ex- Thecompositions treated according to the foregoing process exhibit a marked increase in velocagation.

While the process outlined is one applicable to any such ammonium nitrate explosives containing at least one fusible sensitizing agent, its employment is most desirable in the case of .com-

positions of that type, which are below standard more sensitive, or to such normally cap-sensitive.

explosives that have become insensitive or of doubtful sensitivity due to caking, moisture pickup, or to other reasons. Compositions of this nature include those high in ammonium nitrate and containing a. sensitizing agent which is in liquid .form .at the upper temperature reached. Furthermore, the method may be applied to compositions which are normally insensitive to detonation by a blasting cap, in order to render them cap sensitive. The; method is desirable also in the case of compositions which are normally insensitiveto the action of a blasting cap but which are maintained within such a range of sensitiveness that, while incapable of; detonation by a .cap, they are capable of detonation and of continuous propagation of the explosion when this has once been initiated by, means of a suitable booster charge, and whenused in columns of suflicient diameter. When such compositions are treated by my method, they normally become higher in velocity and of a higher degree of sensitiveness to propagation, though still incapable of detonation by a blasting cap.

I have referred particularly in the foregoing to compositions high in ammonium nitrate and containing a suitable fusible sensitizer or oxygenaccepting ingredient. I find the method particularly effective, however, in the case of compositions such as are described by Kirst and Woodbury in U. S. Patent 1,992,217, where ammonium nitrate is present in an amount higher than 85%, together with at least one fusible sensitizin agent, and where the composition is protected by enclosure in a waterproof container, preferably of metal. As a matter of fact, I find that the effectiveness of my invention is greatly increased by the confinement of the material in a rigid container during the heating step. In such compositions as those of Kirst and Woodbury, the degree of sensitiveness is such that the material can not be detonated by means of a blasting cap or by a line of Cordeau but is capable of detonation and propagation throughout the explosion column with undiminished velocity, when once initiated by a suitable booster charge, provided the column is of sufficiently large diameter. A desirable composition for treatment according to my invention will comprise ammonium nitrate in an amount greater than 85%, 0.5 to 10.0% of a nitrated aromatic hydrocarbon, and 0.5 to 10.0% of a normally solid parafiin hydrocarbon. With such compositions, it is desirable to heat to a temperature at-whichj both sensitizing agents are in liquid form and subsequently to cool to a temperature at which one sensitizer becomes solidified. I

While improved properties result when such compositions are heated and then cooled through the temperature specified, I find that even better results are obtained when the heating and subsequent cooling are repeated several times, so that as many as three or four cycles of successive heating and cooling maybe advantageously carried out.

By way of illustration, a composition comprising 92% ammonium nitrate, 4% dinitrotoluene, and 4% parafiln was enclosed in a tight metal container having soldered seams. The composition had been compressed to an average density of 1.269 and the container was substantially full. The material, at an initial temperature of around 26 C., was heated until atemperature of 50 C. existed throughout, and was then cooled to 30 C. A second cycle consisted of heating to 46 C. and cooling to 31 C., and a third of heating and cooling to 49 C., respectively. The results given below show the effect of the treatment described on the sensitiveness and velocity of the product.

It is apparent from this tabulation that a marked increase in bothvelocity and sensitiveness to propagation is effected with each additional cycle according to the process of my invention.

. cans.

that the method is desirable also in the case of initially good material, in order to make it even more effective.

Table II Maximum spacing in inches for consistent detonation Velocity in Status of composition meters/55mm! Untreateduur After 1 cycle After 2 cycles A similar improvement in both sensitiveness and velocity is shown in this second table, where the material was generally satisfactory before treatment.

It is noteworthy also that the method of treatment described by me has the additional effect of equalizing the density of compositions so heated, when contained in substantially full metal For example, a column of explosive of 5 diameter was tested for density in various portions of its length. Whereas an average density of 1.269 was determined for a can of the untreated material, while a maximum density of 1.286 was found, results for average and maximum densities of similarly packed cans that had been subjected to three treating cycles showed 1.243 and 1.250, respectively. Since high density is frequently a cause of insensitiveness in compressed ammonium nitrate compositions, a method that equalizes density throughout such compositions will be very. advantageous. Actually, of course, the weight of the ammonium nitrate ex plosive in the can of definite volume is unchanged. The fact is that the cans are not completely filled before the heat treatment, since no lowering of density could result if such were the case. Heating causes expansion of the material and tight compression against the walls of the container, as well as substantial equalization of the density throughout. On cooling, contraction doubtless tends to take place, not from the container walls but by means of cracks through the hard material. The process therefore has the further merit of reinforcing the walls of the container against external water pressure, in the case of sub-aqueous shots.

From the foregoing description, it will be apparent that results of great practical utility will be obtained by my invention and that it is applicable to a considerable range of high ammonium nitrate compositions. fective when used with compositions of high density, whether in set or unset condition, and regardless of moisture content, though the presence of water is always undesirable. have described the invention in considerable detail, it will be understood that many variations may be made in the process with respect to minor factors, without departing from the spirit of the invention. I wish to be limited by the following patent claims.

I claim:

1. The method of treating explosive composi- It will be particularly ef-.

While I' tions including ammonium nitrate as the principal ingredient and at least one normally solid fusible organic sensitizing agent, which method comprises enclosing said composition in a substantially filled rigid container, heating the enclosed composition to a temperature at which said sensitizing agent is in liquid state, and subsequently cooling said composition.

2. The method of increasing the sensitiveness to propagation of a relatively high density explo sive composition including ammonium nitrate as the principal ingredient, and at least one normally solid fusible organic sensitizing agent, which method comprises enclosing said composition in a substantially filled rigid container, heating the enclosed composition to a temperature at which said sensitizing agent is in liquid state, and subsequently' cooling said composition.

3. The method of claim 2, in which the sensitizing agent is a nitrotoluene.

4. The method of increasing the sensitiveriess to propagation of an explosive composition of a density greater than 0.90 and comprising more than 85% ammonium nitrate, 0.5 to 10.0% of a nitrated aromatic hydrocarbon, and 0.5 to 10.0% of a normally solid paraffin hydrocarbon, which method comprises enclosing said composition in a substantially filled rigid container, heating the enclosed composition to a temperature at which both the nitrated aromatic hydrocarbon and the paraflin hydrocarbon are in liquid state, and subsequently cooling said composition to a temperature at which at least one of said liquid ingredients becomes solidified.

WILLIAM E. KIRST. 

